I’ve been working on more 4K projects lately and it’s a shame there are no benchmarks for this. My system can handle 4K with no problem but I am in need of speeding things up especially if noise reduction is needed.

Detecting the best combination of performance settings:
running the test data set on up to 12 CPU cores and on up to 1 GPU
AMD Radeon RX 580 Compute Engine: 8192 MB currently available, using up to 90%

If you want to stay with AMD, then RX Vega 64 or R9 Fury might be an option, especially in Windows where GPU drivers work at full speed. Please see this blog post for some figures. Those are for fullHD but the relative differences in speed should be similar for 4k as well.